Raman study of quench products of alkaline carbonate melt at 3 and 6 GPa: Link to the pressure of origin

Abstract

AbstractInclusions of former alkaline carbonate melts occur in igneous minerals, mantle xenoliths, and diamonds from kimberlites and lamproites. However, the identification of most daughter phases remains undetermined owing to the lack of their Raman spectra. Yet, the phase compositions of the alkali carbonate melt at different pressure are interesting to know because Na‐Ca, Na‐Mg, K‐Ca, and K‐Mg double carbonates have a number of pressure‐induced phase transitions. Here, we studied the quench products of K‐Ca, K‐Mg, and Na‐Ca carbonate melts obtained at 3 and 6 GPa. Scanning electron microscopy coupled with energy‐dispersive spectroscopy with silicon drift detector (EDS‐SDD) and Raman spectroscopy were employed for phase characterization. The following carbonates were detected among the quench products: γ‐Na2CO3, Na4Ca(CO3)3 (Ia3d), Na2Ca3(CO3)3 (P1n1), K2Ca(CO3)2 ( ) bütschliite, disordered K2Ca3(CO3)4 (Pnam), K2Mg(CO3)2 ( ), aragonite, magnesite at 6 GPa; and CaCO3‐bearing K2CO3, K2Ca(CO3)2 ( ) bütschliite, K2Ca2(CO3)3 (R3), and ordered K2Ca3(CO3)4 (P212121) at 3 GPa. The results indicate that the quench products of carbonate melt consist of carbonates thermodynamically stable at the pressure of quenching. Thus, the daughter phases in carbonatitic inclusions could be identified by obtained Raman spectra and reflect the pressure conditions of their entrapment.